Method and apparatus for wafer-level micro-glass-blowing

ABSTRACT

A method for forming microspheres on a microscopic level comprises the steps of defining holes through a substrate, disposing a sheet of thermally formable material onto the substrate covering the holes, heating the sheet of thermally formable material until a predetermined degree of plasticity is achieved, applying fluidic pressure through the holes to the sheet of thermally formable material, while the sheet of glass is still plastic, and forming microspheres on the substrate in the sheet of thermally formable material by means of continued application of pressure for a predetermined time. The invention also includes a substrate having a plurality of holes defined therethrough, a layer of thermally formable material disposed onto the substrate covering the plurality of holes, and a plurality of microspheres thermally formed in the layer by means of applied pressure through the holes when it has been heated to a predetermined degree of plasticity.

RELATED APPLICATIONS

The present application is related to U.S. Provisional PatentApplication, Ser. No. 60/721,172, filed Sep. 27, 2005, which isincorporated herein by reference and to which priority is claimedpursuant to 35 USC 119.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to the field of micromachined glass components andmethods of manufacture of the same.

2. Description of the Prior Art

In addition to consumer glass products, glass-blowing is often used tocreate confinement chambers for different types of gases. A normalglass-blowing process is (roughly) as follows:

-   -   Heat the glass to its softening point    -   Remove glass from the heat source (e.g. flame)    -   Immediately apply pressure (blowing) to shape the glass    -   Repeat all steps if needed

In the past, micro-spheres have been fabricated using polymer dropletsthat are allowed to fall through a high column whose temperature profileis controlled by independent heating units, allowing for expansion ofthe spheres. See R. Cook, “Creating Microsphere Targets for InertialConfinement Fusion Experiments”, Energy & Technology Review, pp. 1-9,April 1995; and R. Dagani, “Microspheres Play Role in Medical, Sensor,Energy, Space Technologies”, Chemical and Engineering News, pp. 33-35,December 1994

However, all of these prior efforts have dealt with the fabrication ofspheres that are not attached to any surface and can only be filled withspecific gases during the fabrication process. Small confinementchambers can be achieved by etching (using dry or wet etchant) glass,silicon, or other materials. However, etching usually leads to roughsurfaces as well as very thick sidewalls making it unfit for manyapplications (e.g. when optics need to be integrated with the chamber).Furthermore, it is not possible to achieve a spherical shape withtraditional etching techniques. Large-scale confinement chambers havebeen created in the past using traditional glass-blowing techniques.However, conventional glass-blowing can only be used to create largecomponents (not micro-fabrication compatible).

What is need is a method and apparatus where glass-blowing is performedin a parallel batch process on a microscopic level.

BRIEF SUMMARY OF THE INVENTION

The method of the illustrated embodiment allows for microfabricationcompatible micro-glass-spheres, integrated on a substrate, wafer orchip. These spheres can be filled by gases or other substances postfabrication. In the illustrated embodiment of the invention, the spheresare attached to a wafer, allowing for integration with conventionalmicro-fabrication components and allowing for batch-fabrication ofmicro-glass components.

The invention includes a method for shaping glass on a microscopic scaleto mass-produce multiple glass components, i.e. shaped simultaneously ona micro-scale. This is accomplished by bonding a thin sheet of glass toa perforated wafer, heating the glass, and then blowing the glass fromthe reverse side of the wafer. One potential application of thisinvention is as a confinement chamber for various gases. The chambersare much smaller than traditional glass-blown chambers and aremicro-fabrication compatible.

The invention can be used as a microscopic gas confinement chamber. Manyapplications of this can be considered, e.g. nuclear magnetic resonancegyroscopes, micro-lamps, and hydrogen capsules for H-vehicles. Otherpossible applications include laser fusion targets, as well aslab-on-a-chip, medication capsules, and other biomedical devices.

More specifically, the illustrated embodiment of the invention is amethod for glass-blowing on a microscopic level comprising the steps ofdefining holes through a substrate, such as a semiconductor or siliconsubstrate, wafer or chip, and disposing a sheet of thermally formablematerial, such as glass, onto the substrate covering the holes. Thesheet of thermally formable material is heated, such as by a flame,until a predetermined degree of plasticity is achieved. It must beunderstood that many other forms of heating are contemplated within thescope of the invention, which are both localized to at least some extentto the thermally formable material, such as by a laser, or may beglobal, such as in an oven or heating chamber. Fluidic pressure isapplied through the holes to the sheet of thermally formable material,while the sheet of glass is still plastic. Microspheres are formed orblown on the substrate in the sheet of thermally formable material bymeans of continued application of pressure for a predetermined time.

Preferably the holes are defined by etching using a deep-reactive ionetching (DRIE) method. The step of disposing a sheet of thermallyformable material comprises bonding the thermally formable material tothe substrate using anodic bonding. Again many other different kindsmethods of bonding now known or later devised could be substituted foranodic bonding. In the illustrated embodiment the step of disposing asheet of thermally formable material comprises bonding borosilicateglass to the substrate. The step of defining holes through the substratecomprises etching a plurality of holes through the substrate and formingmicrospheres on the substrate results in simultaneously batchfabricating the microspheres.

The illustrated embodiment of the method further comprises the step offabricating integrated electrical and mechanical components on or intothe substrate, wafer or chip using conventional microfabrication methodsas are now known or as may be later devised as substitutes therefor.

In one embodiment the method further comprises the step of providing anassembly to sandwich the thermally formable material between twoflanges. The assembly comprises a plurality of metal flanges withgaskets in between, screws or any other equivalent means for providing atight seal between the flanges and the substrate, a valve, and a hoseconnected to the valve to allow for the blowing of the thermallyformable material. The blowing of the microspheres is either manuallyperformed or a pressure regulated gas tube is used with the assembly.

In another embodiment the method further comprises selectively heatingof gases or other substances enclosed in the microspheres using aresistive heater integrated on the substrate.

In still another embodiment the method further comprises the step ofdisposing a gas-source material in a solid state in the microspheres andheating the gas-source material to produce a vapor inside themicrospheres.

In one embodiment the method further comprises the step of reducingmagnetic fields introduced by the resistive heater by using two verythin resistive layers in the heater in which the current flows inopposite directions, where the resistive layers are spaced apart by aninsulating dielectric layer.

In still another embodiment the method further comprises the step ofprotecting portions of the thermally formable material that do not coverany holes with a layer of a material with a very high melting point tofunction as a heat shield during blowing and heating.

In the illustrated embodiment the resistive heater is made from amaterial that has a high melting temperature, and the method furthercomprises the step of protecting portions of the thermally formablematerial using the resistive heater as the heat-shield to reduce therisk of undesired deformation of selected areas of the thermallyformable material when heated above its softening point.

In an embodiment the method further comprises the step of protectingportions of the thermally formable material comprises using a protectiveheat-shield separate from the heater.

The invention is also characterized as an apparatus comprising asubstrate, wafer or chip having a plurality of holes definedtherethrough, a layer or sheet of thermally formable material or glassdisposed onto the substrate, wafer or chip covering the plurality ofholes, and a plurality of microspheres thermally formed in the layer orsheet by means of applied pressure through the plurality of holes whenthe thermally formable material or glass has been heated to apredetermined degree of plasticity.

In a further embodiment the apparatus further comprises a selected gas,gases or other substances filling the plurality of microspheres assupplied through the plurality of holes.

In a further embodiment the plurality of holes are sealed from the backonce the microspheres have been filled with gases or other substances.The seal is preferably created by using an adhesive or by anodicallybonding a glass wafer to the back of the silicon wafer. Many othersealing methods now known or later devised could be equivalentlysubstituted.

In other embodiments the apparatus further comprises an integratedelectrical resistive heater disposed on the layer in thermal proximityto the plurality of microspheres.

In an illustrated embodiment the apparatus further comprises a heatshield selectively disposed on the substrate to shield selected portionof the substrate from heat applied to the microspheres.

In the illustrated embodiment the integrated electrical resistive heateris comprised of at least one high temperature resistant layer andfunctions as a heat shield selectively disposed on the substrate toshield selected portions of the substrate from heat applied to themicrospheres.

It must also be understood that the apparatus in other embodimentsfurther comprises at least one micromechanical or microelectrical deviceintegrated into or onto the substrate.

While the apparatus and method has or will be described for the sake ofgrammatical fluidity with functional explanations, it is to be expresslyunderstood that the claims, unless expressly formulated under 35 USC112, are not to be construed as necessarily limited in any way by theconstruction of “means” or “steps” limitations, but are to be accordedthe full scope of the meaning and equivalents of the definition providedby the claims under the judicial doctrine of equivalents, and in thecase where the claims are expressly formulated under 35 USC 112 are tobe accorded full statutory equivalents under 35 USC 112. The inventioncan be better visualized by turning now to the following drawingswherein like elements are referenced by like numerals.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1 a-1 f are cross sectional diagrams illustrating a firstembodiment of the method of the invention.

FIG. 2 is a perspective view of a glass covered substrate, wafer or chipon which a plurality of glass microspheres have been formed.

FIG. 3 is an exploded view of an assembly which is used in oneembodiment to hold the substrate, wafer or chips during fabrication ofthe microspheres in a batch fabrication process.

FIGS. 4 a-4 f are cross sectional diagrams illustrating anotherembodiment of the method of the invention in which a resistiveheater/heat shield is used to heat gas in the microspheres and toselectively protect portions of the substrate, wafer or chips from heatapplied to the microspheres and the glass layer from which they areformed.

The invention and its various embodiments can now be better understoodby turning to the following detailed description of the preferredembodiments which are presented as illustrated examples of the inventiondefined in the claims. It is expressly understood that the invention asdefined by the claims may be broader than the illustrated embodimentsdescribed below.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The illustrated embodiments of the invention was developed as amicroscopic gas confinement chamber, but many other applications areexpressly considered as within the scope of the invention, e.g. vaporcells for nuclear magnetic resonance gyroscopes, micro-lamps, andhydrogen capsules for H-vehicles. Other applications include laserfusion targets, as well as lab-on-a-chip, medication capsules, and otherbiomedical devices. This listing by no means exhausts the list ofpotential uses and applications of the invention.

FIGS. 1 a-1 f depict the illustrated embodiment fabrication process. InFIG. 1 a a photoresist layer 12 is disposed on a substrate 10 andpatterned to define a plurality of openings 14 defined in photoresistlayer 12. Cylindrical holes 16 are then etched in FIG. 1 b all the waythrough a silicon substrate 10, preferably using deep-reactive ionetching (DRIE). The photoresist layer 12 is removed from the top of theperforated substrate 10 as shown in FIG. 1 c. A thin sheet of glass 18(e.g. Pyrex 7740) is then bonded as shown in FIG. 1 d to on top of thesubstrate 10 (e.g. using anodic bonding), covering all of the etchedholes 16. Glass sheet 18 is preferably 50 to 500 μm thick. In theillustrated embodiment a 100 μm thick glass sheet 18 was used. It mustbe expressly understood that the thickness of the sheet 18 is a matterof design chosen according to the teachings of the invention and are notto be understood as limited by the examples given in the illustratedembodiment. Heat (e.g. a flame) is applied from the top side to heat theglass 18 above its softening point. The source of heat is then removedand fluidic or pneumatic pressure is immediately applied from the bottomof the substrate 10. Small, approximately spherical bubbles ormicrospheres 20 in glass sheet 18 will now form on top of the substrate10. The size and thickness of microspheres 20 can be selectivecontrolled by the choice of the diameter and shape of the etched holes16, the thickness of the glass sheet 18, and the time and pressureallowed for pneumatic expansion in the step of FIG. 1 e.

In the step of FIG. 1 f a sealing layer 21 can be disposed on the bottomof substrate 10 sealing holes 16 to trap and maintain the gases or othermaterials that may have been injected or disposed into holes 16 andmicrospheres 20. The composition of layer 21 may be structured accordingto the needs of the application, including providing a selectively gaspermeable or impermeable layer as might be required by the application.

As shown in FIG. 2 multiple microspheres 20 can be batch fabricatedsimultaneously. The fabrication process also allows for potentialintegration of other electrical and mechanical components which may alsofabricated on the substrate 10 using conventional microfabricationtechniques.

One assembly 22 that can be used to assist in the blowing of themicrospheres 20 is illustrated in exploded view in FIG. 3. This assembly22 can be characterized as a pressure chamber that can be used tosandwich the perforated, glass-covered substrate 10, 18 between twoflanges 24 a and 24 b. The assembly 22 is comprised of a number of metalflanges 24 a-24 d with gaskets 26 in between. Screw-holes 28 areprovided in flanges 24 a-24 d to allow for a tight connection and sealbetween the flanges 24 a-24 d and the glass covered substrate 10, 18. Ahose (not shown) is connected to the valved flange 24 d on top to allowfor the actual blowing of the glass microspheres 20. The blowing is doneeither manually or using a pressure regulated gas tube (not shown).

FIGS. 4 a-4 f show a modified fabrication process. In this embodimentthe steps are the same as in the case of FIGS. 3 a-3 f above, but inaddition a resistive heater 34 is integrated on the substrate 10 at FIG.4 d, allowing for post-fabrication heating of the enclosed gases orother substances in microspheres 20 if needed. For example, materialsthat are in a solid state can be heated to achieve a vapor inside themicrospheres 20. In order to reduce the magnetic fields introduced bythe resistive heater 34, two very thin resistive layers 30 a and 30 bare used in which the current flows in opposite directions. Theresistive layers 30 a and 30 b are spaced by an insulating dielectric32. The actual shape of the resistive heater 34 is arbitrary, butpreferentially it is a spiral that encircles an individual glassmicrosphere 20. The step in FIG. 4 f includes the disposition of asealing layer 21 on the bottom of substrate 10 in the same manner asdescribed above in connection with FIG. 1 f.

The glass sheet 18 needs to be heated above its softening point (e.g. bya flame) in order to be able to form the microspheres 20. However, dueto the small size of the microspheres 20, localized heating is very hardto achieve. Instead, the whole substrate 10 will be heatedsimultaneously. Thus, areas that are supposed to stay bonded to thesubstrate 10 and not be affected by the glass-blowing will also beheated. In order to protect the parts of the glass sheet 18 that doesnot cover any holes 16, a layer of a material with a very high meltingpoint can be deposited on top of the glass sheet 18. Many differentmaterials may be used for this purpose, e.g. silicon dioxide, siliconnitride, or indium tin oxide (ITO), which is only a partial list ofsubstitute materials. This material will function as a heat shieldduring the glass-blowing.

If the resistive heater 34 is made from a material that has a highmelting temperature, e.g. ITO, this same layer or layers in heater 34can also function as the heat-shield 36 to reduce the risk of undesireddeformation of certain areas of the glass when it is heated to itssoftening point. Alternatively, separate independent layers are used forthe heater 34 and the protective heat-shield 36.

In summary the illustrated embodiment encompasses within its scope amethod of manufacture and the product made from the method as it relatesto:

-   -   Glass-blowing on a microscopic level    -   Glass-blowing compatible with microfabrication technologies    -   Wafer-level glass-blowing    -   Method for fabricating microspheres    -   Simultaneous manufacturing of numerous microspheres on a chip or        wafer

Many alterations and modifications may be made by those having ordinaryskill in the art without departing from the spirit and scope of theinvention. Therefore, it must be understood that the illustratedembodiment has been set forth only for the purposes of example and thatit should not be taken as limiting the invention as defined by thefollowing invention and its various embodiments.

Therefore, it must be understood that the illustrated embodiment hasbeen set forth only for the purposes of example and that it should notbe taken as limiting the invention as defined by the following claims.For example, notwithstanding the fact that the elements of a claim areset forth below in a certain combination, it must be expresslyunderstood that the invention includes other combinations of fewer, moreor different elements, which are disclosed in above even when notinitially claimed in such combinations. A teaching that two elements arecombined in a claimed combination is further to be understood as alsoallowing for a claimed combination in which the two elements are notcombined with each other, but may be used alone or combined in othercombinations. The excision of any disclosed element of the invention isexplicitly contemplated as within the scope of the invention.

The words used in this specification to describe the invention and itsvarious embodiments are to be understood not only in the sense of theircommonly defined meanings, but to include by special definition in thisspecification structure, material or acts beyond the scope of thecommonly defined meanings. Thus if an element can be understood in thecontext of this specification as including more than one meaning, thenits use in a claim must be understood as being generic to all possiblemeanings supported by the specification and by the word itself.

The definitions of the words or elements of the following claims are,therefore, defined in this specification to include not only thecombination of elements which are literally set forth, but allequivalent structure, material or acts for performing substantially thesame function in substantially the same way to obtain substantially thesame result. In this sense it is therefore contemplated that anequivalent substitution of two or more elements may be made for any oneof the elements in the claims below or that a single element may besubstituted for two or more elements in a claim. Although elements maybe described above as acting in certain combinations and even initiallyclaimed as such, it is to be expressly understood that one or moreelements from a claimed combination can in some cases be excised fromthe combination and that the claimed combination may be directed to asubcombination or variation of a subcombination.

Insubstantial changes from the claimed subject matter as viewed by aperson with ordinary skill in the art, now known or later devised, areexpressly contemplated as being equivalently within the scope of theclaims. Therefore, obvious substitutions now or later known to one withordinary skill in the art are defined to be within the scope of thedefined elements.

The claims are thus to be understood to include what is specificallyillustrated and described above, what is conceptionally equivalent, whatcan be obviously substituted and also what essentially incorporates theessential idea of the invention.

1. A method for glass-blowing on a microscopic level comprising:defining holes through a substrate; disposing a sheet of thermallyformable material onto the substrate covering the holes; heating thesheet of thermally formable material until a predetermined degree ofplasticity is achieved; applying fluidic pressure through the holes tothe sheet of thermally formable material, while the sheet of glass isstill plastic; and forming microspheres on the substrate in the sheet ofthermally formable material by means of continued application ofpressure for a predetermined time.
 2. The method of claim 1 wheredefining the holes comprises etching the holes using deep-reactive ionetching (DRIE).
 3. The method of claim 1 where disposing a sheet ofthermally formable material comprises bonding the thermally formablematerial to the substrate using anodic bonding.
 4. The method of claim 1where disposing a sheet of thermally formable material comprises bondingborosilicate glass to the substrate.
 5. The method of claim 1 wheredefining holes through the substrate comprises etching a plurality ofholes through the substrate and forming microspheres on the substratecomprises simultaneously batch fabricating the microspheres.
 6. Themethod of claim 1 further comprising fabricating integrated electricaland mechanical components on or into the substrate.
 7. The method ofclaim 1 further comprising providing an assembly to sandwich thethermally formable material between two flanges, the assembly comprisinga plurality of metal flanges with gaskets in between, screw means forproviding a tight seal between the flanges and the substrate, a valve, ahose connected to the valve to allow for the blowing of the thermallyformable material, wherein the blowing is either manually performed or apressure regulated gas tube is used.
 8. The method of claim 1 furthercomprising selectively heating of gas, gases or other substancesenclosed in the microspheres using a resistive heater integrated on thesubstrate.
 9. The method of claim 1 further comprising disposing agas-source material in a solid state is disposed in the microspheres andheating the gas-source material to produce a vapor inside themicrospheres.
 10. The method of claim 1 further comprising sealing themicrospheres by bonding a layer to a bottom of the substrate.
 11. Themethod of claim 8 further comprising reducing magnetic fields introducedby the resistive heater by using two very thin resistive layers in theheater in which the current flows in opposite directions, where theresistive layers are spaced apart by an insulating dielectric layer. 12.The method of claim 1 further comprising protecting portions of thethermally formable material that do not cover any holes with a layer ofa material with a very high melting point to function as a heat shieldduring blowing and heating.
 13. The method of claim 8 where theresistive heater is made from a material that has a high meltingtemperature, and further comprising protecting portions of the thermallyformable material using the resistive heater as the heat-shield toreduce the risk of undesired deformation of selected areas of thethermally formable material when heated to its softening point.
 14. Themethod of claim 8 further comprising protecting portions of thethermally formable material comprises using a protective heat-shieldseparate from the heater.
 15. An apparatus comprising: a substratehaving a plurality of holes defined therethrough; a layer of thermallyformable material disposed onto the substrate covering the plurality ofholes; and a plurality of microspheres thermally formed in the layer bymeans of applied pressure through the plurality of holes when thethermally formable material has been heated to a predetermined degree ofplasticity.
 16. The apparatus of claim 15 wherein the layer of thermallyformable material is composed of glass.
 17. The apparatus of claim 15further comprising a selected gas, gases or other substance filling theplurality of microspheres as supplied through the plurality of holes.18. The apparatus of claim 15 where the substrate has a bottom andfurther comprising a layer disposed on the bottom of the substrate toseal the microspheres.
 19. The apparatus of claim 15 further comprisingan integrated electrical resistive heater disposed on the layer inthermal proximity to the plurality of microspheres.
 20. The apparatus ofclaim 15 further comprising a heat shield selectively disposed on thesubstrate to shield selected portion of the substrate from heat appliedto the microspheres.
 21. The apparatus of claim 19 where the integratedelectrical resistive heater is comprised of at least one hightemperature resistant layer and functions as a heat shield selectivelydisposed on the substrate to shield selected portion of the substratefrom heat applied to the microspheres.
 22. The apparatus of claim 15further comprising at least one micromechanical or microelectricaldevice integrated into or onto the substrate.